Small firm makes the big corrections

RICHMOND, Calif. -- When NASA needed small corrector mirrors to bring sharp focus to the Hubble Space Telescope, it recruited some of the nation's biggest high-technology corporations to make them.

Kodak declined to take on the task of grinding such convoluted mirrors, and Hughes and United Technologies could not meet the agency's strict schedule and billionths-of-an-inch specifications.

Almost as an afterthought, the National Aeronautics and Space Administration turned to Tinsley Laboratories.

The obscure company, hidden behind a shopping mall in this blue-collar San Francisco suburb, mainly made custom lenses for the electronics industry. But scientists at the Jet Propulsion Laboratory in Pasadena, Calif., knew it also supplied optics for Voyager spacecraft and mirrors for the Keck telescopes in Hawaii.

Despite the daunting complexity and uncompromising requirements of the job, Tinsley, using computer-controlled grinding and polishing machines built by its own employees, turned out 36 mirrors on time, under budget -- and well within NASA's stringent design standards.

Eight of the mirrors, tucked inside a new wide-field and planetary camera, were installed by astronauts Monday night. Ten more, part of an instrument called Corrective Optics Space Telescope Axial Replacement, or COSTAR, were to be put into Hubble last night. The remaining 18 mirrors are duplicates stored at NASA's Goddard Space Flight Center in Greenbelt, Md.

Tinsley executives here and NASA officials in Washington are confident the new mirrors will fully correct Hubble's sight and permit astronomers to see deeper into space.

Two repair packages are being installed in the Hubble telescope by spacewalking astronauts.

The packages themselves are each roughly the size of a telephone booth, but the mirrors inside are only as big as the coins required to make a call. Since even tiny defects may significantly distort images in such small mirrors, NASA decided the mirrors must be ground to within 10 Angstrom units (an Angstrom is four-billionths of an inch) of perfection.

Tinsley's mirrors are perfect to within six Angstroms.

"That means there are only a few atoms out of place," said James Crocker, the NASA engineer in charge of designing one of the two packages.

Tinsley President Bob Aronno said such tolerances test the limit of today's technology, both in polishing fused-silicate glass to such precision and being able to detect such minuscule flaws.

The difficulty was compounded because the Hubble repair team needed mirrors that were aspherical -- that is, their concave surface is slightly steeper at the edges than it is toward the center, to compensate for an opposite error in the space telescope's famously flawed 96-inch main mirror.

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